Various methods have been proposed for production of hydrogen H2 on an industrial scale. In a natural gas reformation method using natural gas as raw material, H2 is obtained by reforming the natural gas with water vapor, in the presence of a catalyst, into hydrogen H2 and carbon monoxide CO and converting the resultant CO, through a water gas shift reaction, into H2 with carbon dioxide CO2 as by-product which in turn is removed. In order to obtain heat required for the reformation reaction which is endothermic, a small amount of oxidizer (oxygen or air) is added for combustion of a portion of the natural gas to thereby obtain heat required.
The above-mentioned natural gas reformation method uses expensive natural gas as raw material. In addition, securement of the raw material itself is becoming difficult in a current situation where demand for natural gas is progressively increasing. Furthermore, production of CO2 as by-product in the reformation process is undesirable from a viewpoint of reduction of greenhouse gas discharge. Such discharge of the by-product CO2 may be suppressed by adding a device for recovery of the by-product CO2, which is however problematic in that not only the raw material itself is expensive but also processing cost is increased for concentrating and removing of CO2, inevitably resulting in elevation in price of hydrogen as end product.
A gasification method using coal or heavy oil as raw material is fundamentally similar to the natural gas reformation method. Coal or heavy oil is reacted with water vapor in the presence of a small amount of oxidizer into H2 and CO, the resultant CO being converted into H2 and CO2 by the water gas shift reaction.
With this gasification method, coal or heavy oil as raw material is cheaper than natural gas. However, it is problematic in that not only proportion of carbon C in elemental composition of the raw material is greater than that of natural gas, but also high temperature (1000° C.-1500° C., depending on reaction method) is required for the reaction, so that burned proportion of the raw material becomes greater and thus a discharged amount of CO2 becomes greater.
In order to overcome this, a CO2 recovery type gasification system called HyPr-RING process has been recently proposed an example of which is disclosed in Patent Literature 1.
In the CO2 recovery type gasification line, H2 is obtained by reacting a carbon-containing raw material such as coal or biomass with water vapor H2O in the presence of calcium oxide CaO as CO2 absorbent. CO2 produced during the reaction is fixed as calcium carbonate CaCO3 (absorptive-reaction product) by the co-existing CaO and further CO is converted into CO2 and H2 by the water gas shift reaction, so that H2 becomes prevailing in the gasified gas produced. CH4 and other hydrocarbons are also produced and contained without change in the gasified gas since they do not react with CaO. CH4 produced is in an amount around 10% to 20% of that of H2, the other gas components being in extremely small amounts.
The absorptive-reaction product CaCO3 fixed through absorption of CO2 is burned at high temperature for separation of CO2 (this is termed as “calcination”), CaO obtained by the CO2 separation being reused. Such calcination performed in the mixed gas of CO2 with oxygen O2 brings about highly concentrated CO2 and therefore facilitates recovery and isolation of CO2.                [Patent Literature 1] JP 2003-82361A        